XXI.] THE COLOUR OF BLOOD. RESPIRATION. 221 



broken-up corpuscles. Mount a little of the 

 sediment and examine under a high power. 

 Note 



a. The crystals of haemoglobin (oxyhaemo- 

 globin); those of the rat are thin rhombic 

 prisms ; those of the guinea-pig are ap- 

 parently tetrahedra but in reality belong also 

 to the rhombic system. Look for a clump of 

 crystals to observe better their bright red 

 colour. 



b. The decolorized red blood corpuscles; these 

 will be seen as pale rings mixed up with 

 a good deal of granular debris. 



Sometimes defibrinated guinea-pig's blood yields 

 crystals when a drop of it is simply mounted 

 with a drop of chloroform ; usually crystals may 

 be obtained without leaving the blood for a day 

 in the cool by placing a little of the frozen blood 

 on a slide, putting on a cover-slip, warming 

 gently over a flame for about half a minute and 

 then cooling; as the blood cools crystals separate 

 out 



3. Let blood (a large quantity is best) clot in a 

 beaker, leave it for a day, then pour off the 

 serum, mince the clot and shake the fragments 

 gently with an equal volume of cold water, place 

 a piece of muslin over the beaker and pour off 

 the fluid; repeat this two or three times, then 

 treat the residue with about three times its 

 volume of water (best at temperature of about 



